This invention is directed to a device for producing a mass separated ion beam which is finely focused and which has selectable energy. This direct-write ion beam may be used for directly writing on a semiconductor target to produce a semiconductor device without the use of masks.
Conventional ion implantation has emerged from research into manufacturing. In the conventional ion implantation, a broad approximately 1 cm in diameter ion beam is raster scanned over a wafer to create a uniformly implanted layer. Pattern definition is achieved through conventional masking (as by lithography) which involves a thin film of silicon dioxide or sometimes metal over the substrate.
Using focused ion beams is an elegant technique for microfabrication in that it eliminates conventional masking and wet process steps. The basic idea behind the focused ion beam is the elimination of all masking steps. The beam should therefore be focused sufficiently so that implantation patterns can be written by programming the beam deflection and blanking the beam. Prior effort at providing a finely focused ion beam with sufficient energy for implantation was not successful. Prior effort by R. L. Seilger and W. P. Fleming, as published March 1974 in the Journal of Applied Physics, Volume 45 Number 3, produced microprobes with about 5 micrometer spot diameter and with a maximum beam energy of about 60 kV. Such beams had current which was too low for most applications. Another example of early work is George Brewer, U.S. Pat. No. 3,585,397. Brewer was unable to provide a high brightness, small diameter ion source. Instead, Brewer flooded ions onto a small aperture and imaged the aperture at the target. In that structure the ion current was too low to be useful for practical implantation. Thus, there have been no devices capable of satisfactory direct writing ion implantation beams of sufficient current and sufficiently small diameter at the target for use in modern day semi-conductor development and manufacture.